a) Field of the Invention
The invention is directed to a geodetic instrument with a telescope F whose sighting axis ZA has a common intersection point S with a tilt axis KA and a rotational axis DA about which the telescope F is swivelable and in which, further, a laser arrangement is provided which is used for aligning the rotational axis DA over the ground point and for determining the height h of the intersection point S over the ground point.
b) Description of the Related Art
Geodetic instruments of this type, e.g., theodolites or tachymeters, are known. They are used for land surveying based on determination of horizontal and vertical angles and, for this purpose, are generally set up by means of a tripod, e.g., over a boundary mark. In principle, they comprise an upper part which is swivelable about the vertically oriented rotational axis DA (often also called the vertical axis) and carries a telescope which can transit around the tilt axis KA with cross hair and distance adjustment in a sighting axis ZA which, like the rotation axis DA and the tilt axis KA, intersects the intersection point S.
For example, DE 38 38 512 describes a theolodite in which the carrying plate of the stand to which the theolodite is fitted has a cutout in its center through which a laser beam can be directed along the rotational axis to the ground point with which the theolodite is to be aligned. This provides an optical sighting device which facilitates setup and orientation.
However, this orientation of the device is not adequate for very precise measurements; rather, it is also necessary to know the height of the instrument, i.e., the height h of the intersecting point S of the sighting axis ZA, tilt axis KA and rotational axis DA over the ground point.
In this connection, DE 198 02 379 A1 discloses a surveying instrument with various accessories, including auxiliary means for determining the instrument height. For this purpose, a prism is to be placed on the ground point and an auxiliary mirror is swiveled in front of the telescope with a horizontally oriented sighting axis, so that the distance from the ground point can be measured with the electrooptical distance meter of the instrument and the instrument height can accordingly be determined.
Further, DE 40 07 245 A1 describes a xe2x80x9cdevice for centering a geodetic instrumentxe2x80x9d over a defined ground point by means of an optical sighting device which is arranged centric to the vertical axis of the instrument. Again, as was mentioned above, this sighting device has means for generating a visible collimated laser beam bundle and means for projecting the bundle on to the ground point located in the extension of the vertical axis of the geodetic instrument. In this case, however, it is suggested that the laser beam bundle be utilized additionally for measuring the height between the ground point and the sighting axis.
The description of this device shows only that the laser beam bundle is modulated, the light reflected from the ground point is guided back to a reception device and the distance between the ground point and sighting axis is determined in an evaluating device following the reception device. The distance between the ground point and sighting axis is calculated from the reception signal. It is disadvantageous that distance measuring devices of this type are technically complicated and therefore cost-intensive.
Proceeding from this prior art, it is the primary object of the invention to further develop a geodetic instrument of the type mentioned above in such a way that the centering of the device and the determination of the height of the intersecting point of sighting axis, swiveling axis and rotational axis over the ground point are ensured economically with respect to instrument technology, with high accuracy and favorable ergonomics.
According to the invention, a first, preferably collimated, laser beam extending in the rotational axis DA and at least one further laser beam path which is divergent relative to the first laser beam are provided and enclose an angle xcex3. Further, a measuring device for determining the distance a between the two laser beam paths at the height of the ground point and an evaluating device for calculating the height h of the intersection point S over the ground point from the relationship hxcx9ca at a known angle xcex3 are provided. The distance a is measured in the horizontal or at a right angle to the rotational axis DA.
This arrangement enables the determination of the distance between the ground point and the intersection point S on the basis of a measurement triangle which is formed by the first collimated laser beam, at least one further laser beam path enclosing a preferably constant angle xcex3 with the first laser beam, and the distance a. The relationship hxcx9ca corresponds to a basic trigonometric function.
The essential advantage of the invention consists in the possibility of relatively low expenditure on construction because fewer subassemblies are required than in a device outfitted with an optoelectronic distance measuring device according to the prior art.
An advantageous construction of the laser arrangement provides a housing which is arranged with its longitudinal axis radial to the rotational axis DA, a laser arranged in the housing, an objective which is likewise arranged in the housing for bundling the laser beam, and a deflecting element following the objective outside the housing for coupling the laser beam into the rotational axis DA; further, the laser arrangement according to the invention has optical means for generating the divergent laser beam path.
There are different possible variants for designing the optical means mentioned above. For example, they can be constructed such that a diffractive element with an optically active structure is disposed in the first laser beam so that a proportion of this radiation is transformed into a circular diffraction pattern oriented concentric to the rotational axis DA and this circular diffraction pattern is directed divergently onto the ground point or its neighborhood.
The diffractive element is arranged in front of or behind the deflecting element in the beam path and comprises a transparent plate which is provided with a pattern hologram. The pattern hologram is formed of geometric figures which are preferably formed from points arrayed in a circular shape, line shape and/or over a surface area. The figures are arranged centric to the laser beam and have a brightness maximum in their center.
This brightness maximum can be formed by a centrally situated surface area portion with the highest possible transparency or also by a central cutout in the transparent plate.
As an alternative to the construction variant mentioned above, at least one additional laser light source can be provided for generating the divergent laser beam path; this additional laser light source radiates into the objective at an angle xcex1xe2x89xa00xc2x0 and is imaged through the objective onto the ground point or its neighborhood, wherein the beam path directed to the ground point encloses with the first laser beam the divergence angle xcex3 which is proportional to the incident angle xcex1.
In this respect, a particularly preferable construction of the invention consists in that a first laser diode is arranged in such a way that the radiation proceeding from it is radiated into the objective in the direction of the optical axis, i.e., at an angle xcex1=0xc2x0, wherein the light emitted by it is used to generate the first laser beam and accordingly serves primarily for centering the geodetic device.
In addition to this first laser diode, two additional laser diodes are provided, each of which radiates into the objective at an angle xcex1xe2x89xa00xc2x0, preferably where xcex1xe2x89xa00xc2x0.
The two laser diodes radiating into the objective at an angle xcex1xe2x89xa00xc2x0 generate two laser beams, each of which encloses a divergence angle xcex3 with the first laser beam. In this way it is achieved that each of the three laser light sources is imaged on the ground point or in its immediate neighborhood, wherein the three laser diodes are so arranged in relation to the objective that their three images lie on a straight line. The center image is used for centering and the distances a between the two outer images and the center image at a known angle xcex3 is a measure for the height h of the intersection point S above the ground point.
Addition constants which are given, for example, by the difference in height caused by technical factors relating to the instrument between the vertex of the divergent beam paths and the intersection point S can, of course, be included in the determination of this height h.
Alternatively, a scale which is constructed for visually reading the distance a or sum 2a and which is provided with a bar code or bar marking calibrated in a unit of length or a position-sensitive optoelectronic detector followed by an evaluating and display device can be provided as measuring device.
The distance a can be determined in a simple manner with the scale by placing it on the ground point in such a way that the first laser beam or the image of the first radiation source is directed to the bar marking and then, by means of the bar marking, reading off the diameter d=2a of the circular diffraction pattern or the distance a of the images of the second and first radiation source from the image of the first radiation source.
A particularly advantageous construction of the invention is provided in that (at a constant angle xcex3) the bar marking is calibrated in a manner deviating from the metric unit such that an amount for height h can be read off directly.
CCD lines or CCD arrays, for example, can be provided as position-sensitive detectors. The maximum distance between two radiation sources imaged on the array or on the CCD line is an equivalent for the height h, wherein it is likewise a prerequisite in this case that the three images lie on a straight line.
A value for the height h can be obtained in signal processing means, known per se, from the maximum distance 2a between the two outer images on the detector and is shown on a display. A CCD line and a display can advantageously be accommodated on a compact unit, for example, in the form of a flat measurement instrument.
In order to determine the height h, it is then only necessary to place this flat measurement instrument on the ground point and to ensure that the first laser beam impinges on the CCD line and that the two outer beam paths are imaged on the CCD line, whereupon a value for height h can be read directly from the display.
For the sake of completeness, it is noted that the radiation sources and the laser diodes emit a radiation in the visible wavelength range of light with an intensity which can be detected very well also when daylight is superimposed.
The invention will be described more fully in the following with reference to an embodiment example.